In a wireless communications system such as a mobile cellular communications system, a wireless local area network (WLAN), or fixed wireless access (FWA), a communication node such as a base station (BS), an access point (AP), a relay station (RS), or user equipment (UE) generally has a capability of transmitting a signal of the communication node itself and a capability of receiving a signal from another communication node. As a wireless signal is greatly attenuated in a radio channel, compared with a signal transmitted by a communication node itself, a signal from a communication peer end is extremely weak when arriving at a receive end. For example, in a mobile cellular communications system, a difference between power of a receive signal of a communication node and power of a transmit signal of the communication node reaches 80 dB-140 dB or is even larger. Therefore, to avoid self-interference caused by a transmit signal on a receive signal of a same transceiver, sending and receiving of a wireless signal are generally distinguished by using different frequency bands or time periods. For example, in frequency division duplex (FDD), different frequency bands that are separated by a specific protection frequency band are used to perform communication during sending and receiving; in time division duplex (TDD), different time periods that are separated by a specific protection time interval are used to perform communication during sending and receiving, where a protection frequency band in an FDD system and a protection time interval in an TDD system are to ensure that receiving and sending are fully separated, to avoid interference caused by sending to receiving.
Different from those in an existing FDD or TDD technology, in a wireless full-duplex technology, receiving and sending operations may be simultaneously performed on a same radio channel; in this case, theoretically, spectral efficiency of the wireless full-duplex technology is twice that of the FDD or TDD technology. Obviously, a premise for implementing wireless full-duplex lies in avoiding, reducing, and canceling as much as possible strong interference (which is called self-interference) caused by a transmit signal on a receive signal of a same transceiver, so that the transmit signal does not affect correct receiving of a desired signal.
FIG. 1 is a schematic block diagram of an interference suppression principle of an existing wireless full-duplex system, where a DAC (digital-to-analog converter), up-conversion, and power amplification that are of a transmit path, a low noise amplifier (LNA), down-conversion, and an ADC (analog-to-digital converter) that are of a receive path, and the like are functional modules of an intermediate frequency/radio frequency unit in an existing transceiver. Cancellation of self-interference caused by a transmit signal is completed by using units such as space interference suppression, analog interference cancellation at a radio frequency front-end, digital interference cancellation, and the like shown in the figure.
Because strength of a self-interference signal in a receive signal that undergoes space interference suppression is far greater than strength of a desired signal, the receive signal may cause block of an LNA module and the like at a receiver front-end. Therefore, before the LNA, the analog interference cancellation module at the radio frequency front-end uses, as a reference signal, a coupled radio frequency signal that undergoes power amplification at a transmit end, and the reference signal is adjusted by using an estimated parameter such as amplitude and a phase of a channel from a local transmit antenna to a receive antenna, so that the reference signal is as close as possible to a self-interference signal component in the receive signal, thereby canceling, in an analog domain, a local self-interference signal received by the receive antenna.
As shown in FIG. 1, in the existing wireless full-duplex system, radio frequency analog self-interference suppression is completed before the LNA. However, besides a main-path self-interference signal component formed when a transmit signal arrives at a transmit antenna from a receive antenna by means of line-of-sight (LOS) propagation, the transmit signal propagated in space may also enter the receive antenna after being transmitted by a scatterer; in this case, a self-interference signal further includes other components such as a near-field reflected self-interference signal and a far-field reflected self-interference signal.
FIG. 2 shows composition of a self-interference signal. As shown in FIG. 2, power of a far-field reflected self-interference signal component is extremely small. Therefore, the far-field reflected self-interference signal component does not affect a receive path after an LNA, and interference cancellation may be performed on a base band by using a digital filter after an analog-to-digital converter (ADC). However, power of a near-field reflected self-interference signal component is relatively large, which may cause saturation of a receiver after the LNA.
Therefore, it is expected to provide a technology that can cancel a near-field reflected self-interference component.